Proteomic study of 6-OHDA-induced neurodegeneration of rat nigrostriatal pathway

Background: The aetiology of Parkinson's disease (PD), an age-related disorder characterized by a progressive degeneration of dopaminergic neurons of the substantia nigra (SN) pars compacta, remains unclear. Current treatments, such as administration of L-DOPA, are only symptomatic and do not stop or delay the progressive loss of neurons. In fact, it has been suggested that the dopamine precursor L-DOPA, increases generation of reactive oxygen species (ROS) leading to further neuronal damage. A similar loss in nigro-striatal dopaminergic neurons is produced on intracerebral administration of the catecholaminergic neurotoxin 6-hydroxydopamine (6-OHDA). In this animal model of PD, termed 'the hemi-parkinsonian rat', unilateral injection of 6-OHDA into the nigro-striatal pathway results in extensive loss of dopaminergic cells in the ipsolateral SN. In an attempt to identify some of the proteins that are involved in dopaminergic neuronal death, we used the proteomic methods to analyze this animal model of PD. Methods: Five hemiparkinsonian rats were obtained by intranigral stereotaxic injection of 6-OHDA. The right 6-OHDA-lesioned substantia nigra and striatum tissues along with the left, unlesioned controlateral tissues, were excised and homogenized, using urea-based buffer, to extract the tissues protein. The separation of the protein mixtures and the visualization of the protein patterns obtained were performed using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Protein profiles of control and treated tissues were compare by the PDQuest 2D-gel analysis software (BIO-Rad Lab., Hercules, CA, USA). The protein spots showing differential expression were analysed by matrix assisted laser desorption/ionizing time of flight (MALDI-TOF) mass spectrometry. Results: The brain protein extraction and solubilization protocol was validated obtaining a satisfactory protein profile. In comparison to the normal rats, emiparkinsonian animals exhibited a different expression in alpha-enolase and beta-actin in substantia nigra and striatum, respectively. Conclusion: The proteomic study of rats unilateral injection of 6-OHDA into the nigro-striatal tissues allowed us to identify two proteins, alpha-enolase and beta-actin, showing increased levels in the 6-OHDA-lesioned brain tissues compared to control. Previous studies described the same proteins as oxidized and proteins in Alzheimer's disease (AD) brain. Our preliminary data could mirror those results pointing out a common mechanism of neurodegenerative diseases.